1. Field of the Invention
The present invention relates to an apparatus for the mixing and dispensing of expanding foams and, more particularly, to an improved foam dispensing gun and system having improved spray characteristics and methods for the same.
2. Description of the Related Art
Various foam dispensing devices or guns have been proposed and used for the mixing and dispensing of expanding synthetic foams, such as polyurethane or polyisocyanurate foams. The preparation of many expanding synthetic foams requires uniform mixing of two fluid components, liquid organic resins with polyisocyanates, in a mixing chamber. When these two components are mixed in proper proportions, they typically react quickly to form and solidify into an expanded foam. Foam dispensing guns must, therefore, be kept free from buildup of the foam components and resulting expanded foam, so that control valves and passageways do not become clogged, rendering the foam dispensing gun inoperable.
Certain prior foam dispensing guns required dismantling after each application in order to clean the dispenser. More recently, most foam dispensing guns have utilized integral means for cleaning purposes, with a solvent being introduced to the foam dispensing gun after each use to flush the expanded foam and unreacted foam components therefrom. However, experience with foam dispensing guns of this general nature has shown that adequate cleaning is not always provided. Thus, frequent disassembly of the foam dispensing gun to remove the residue foam is still required which reduces the efficiency of the foam installation operation. Furthermore, foam dispensing guns of this type introduce additional problems of toxicity and disposal of the solvent.
There are two types of foam dispensing guns: "pour" guns and spray guns. Pour guns are used for various applications which include packaging objects for shipping, cavity fill for floatation and/or cavity fill for insulation. A pour gun, as the name suggests, simply pours the mixed foam into a desired cavity to accomplish the necessary application. Typically, the steps involved in packaging an object consists of initially directing a "shot" of-the mixed foam into the bottom of the container, inserting a polyethylene sheet over the top of the shot of mixed foam, placing the object to be shipped in the container, placing another sheet of polyethylene on top of the object, and then dispensing more mixed foam to fill the container with the cushioning foam. A delay of 10-20 seconds from the time the first shot is dispensed to the time the second shot is dispensed allows the accumulation of foam to harden and possibly clog the foam dispensing gun. Thus, pour guns must be suitably adapted to handle frequent shots of mixing foam of brief duration without clogging.
Spray guns are used to apply polyurethane foam as insulation to walls of vessels or various components. The spray gun is used to emit a continuous, uniform spray of foam over a given surface. Thus, the spray gun must be suitably adapted to emit the spray of foam from the foam dispensing gun for extended periods of time without interruption. Also, depending on the foam application, the foam dispensing gun should be capable of dispensing a quality foam spray over a range of spraying distances.
Due to the varied uses of foam dispensing guns, it may be necessary to apply polyurethane foam or polyisocyanurate foam over large areas covering considerable distances. It is desirable to be able to apply the foam with a minimum of interruptions without the need to frequently move the entire foam dispensing system while keeping the system simple to maintain and inexpensive to operate.
It is desirable to be able to vary the ratio of the two components forming the foam to accomplish solidified foam having desired physical properties.
It is also desirable to be able to adjust the "fineness" of the spray pattern of the foam without adjusting the pressure of the foam components supplied to the foam dispensing gun.
Another problem with certain prior foam dispensing guns is that the nozzle through which the mixed foam exits the gun clogs after the pouring or spraying ceases. Thus, the nozzles, typically made from plastic, need to be replaced after each usage. This is both time consuming and costly. It is desired to have a foam dispensing gun which cleans and removes mixed foam from the nozzle during and after each use.
Many foam dispensing guns require the foam components to be under high pressure, on the order of 800-1200 pounds per square inch, during the spraying operation. The high pressure of the foam components mixes the foam components and propels the mixed foam from the foam dispensing gun in a finely atomized mist. The high pressure is augmented by heating the hoses which deliver the components to the foam dispensing gun. The heat added to the components improves the mixing of the foam components and the resulting volume of produced foam. However, the high operating pressures and heat requirement adds to the cost and maintenance of the foam dispensing system. It is desirable to have a foam dispensing gun which operates at low pressures without the need of heating the hoses.